This project is on the interaction of tumor cells and host defense cells. Current studies are on the depression of macrophage chemotaxis and increase in macrophage phagocytosis that occurs in experimental animals and on the increase in phagocytic response that occurs when serum from tumor-bearing mice is transferred to normal mice; mechanisms of macrophage activation and the impairment of activation in certain strains of mice; production of lymphotoxin by subpopulations of spleen cells.